The growing dependency on renewable energy sources and the wide range of electrical loads in residential and industrial applications, demands the next generation of power electronics circuits to be more flexible and capable of transferring electrical power from any types of source, including dc, single-phase ac, or multi-phase ac, to any type of load (dc, single-phase ac, or multi-phase ac) without compromising reliability, cost, efficiency, or power density. There are numerous applications in which the instantaneous values of input and output power are not equal. For instance, in a single-phase inverter the input current and voltage are ideally both dc, resulting in a constant dc power; whereas, the load power has a dc component and an alternating component the frequency of which is twice the frequency of the load voltage/current. The alternating part of the load power will result in the appearance of a double frequency current harmonic at the dc-side, if it is not suppressed. The presence of double frequency harmonic component at the dc-side current is undesirable and can deteriorate the performance of the system. Similarly, in a single-phase ac to single-phase ac converter, the instantaneous values of input and output power will not be the same if the input and output frequencies do not match. Moreover, the instantaneous power of a three-phase system will be dc; therefore interfacing a single-phase system and a three-phase ac system will also results in the appearance of the double frequency harmonic.
The most dominant solution for suppressing the double frequency harmonic is filtering it through a large (high capacitance) capacitor. Electrolytic capacitors are available at high capacitances; however, they have very high failure rates, and are considered the leading cause of failures in power electronic circuits. The failure rates of the other types of capacitors, i.e. film and ceramic capacitors, are much lower than that of electrolytic capacitors; however, they are not available at high capacitances.